Aquarium filter



FIG. 1 is an isometric view of the filter taken from the top;

FIG. 2 is an isometric view of the filter taken from the bottom;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for an aquarium filter, as shown. 